Trimetallic reforming catalyst

ABSTRACT

A novel trimetallic catalytic composite, a method of manufacture and process use thereof is disclosed. The composite comprises a refractory support having a nominal diameter of at least 650 microns and having deposited thereon a uniformly dispersed platinum component, a uniformly dispersed tin component and a surface-impregnated metal component selected from the group consisting of rhodium, ruthenium, cobalt, nickel, iridium and mixtures thereof. When this catalytic composite is used in the reforming of hydrocarbons at low pressures significant improvements in activity stability is observed compared to catalysts of the prior art.

BACKGROUND OF THE INVENTION

The subject of the present invention is a novel trimetallic catalyticcomposite which has exceptional activity and resistance to deactivationwhen employed in a hydrocarbon conversion process that requires acatalyst having both a hydrogenation-dehydrogenation function and acracking function. More precisely, the present invention involves anovel dual-function trimetallic catalytic composite which, quitesurprisingly, enables substantial improvements in hydrocarbon conversionprocesses that have traditionally used a dual-function catalyst. Inanother aspect, the present invention involves improved processes thatare produced by the use of the novel catalytic composite, specifically,an improved reforming process which utilizes the subject catalyst toimprove activity, selectivity, and stability characteristics.

Composites having a hydrogenation-dehydrogenation function and acracking function are widely used today as catalysts in many industriessuch as the petroleum and petrochemical industry to accelerate a widespectrum of hydrocarbon conversion reactions. Generally, the crackingfunction is thought to be associated with an acid-acting material of theporous, adsorptive, refractory oxide type which is typically utilized asthe support or carrier for a heavy metal component such as the metals orcompounds of metals of Groups V through VIII of the Periodic Table towhich are generally attributed the hydrogenation-dehydrogenationfunction.

These catalytic composites are used to accelerate a wide variety ofhydrocarbon conversion reactions such as hydrocracking, isomerization,dehydrogenation, hydrogenation, desulfurization, cyclization,alkylation, polymerization, cracking, hydroisomerization, etc. In manycases, the commercial applications of these catalysts are in processeswhere more than one of these reactions are proceeding simultaneously. Anexample of this type of process is reforming wherein a hydrocarbon feedstream containing paraffins and naphthenes is subjected to conditionswhich promote dehydrogenation of naphthenes to aromatics,dehydrocyclization of paraffins to aromatics, isomerization of paraffinsand naphthenes, hydrocracking of naphthenes and paraffins and the likereactions to produce an octane-rich or aromatic-rich product stream.Another example is a hydrocracking process wherein catalysts of thistype are utilized to effect selective hydrogenation and cracking of highmolecular weight unsaturated materials, selective hydrocracking of highmolecular weight materials, and other like reactions, to produce agenerally lower boiling, more valuable output stream. Yet anotherexample is an isomerization process wherein a hydrocarbon fraction whichis relatively rich in straight-chain paraffin compounds is contactedwith a dual-function catalyst to produce an output stream rich inisoparaffin compounds.

Regardless of the reaction involved or the particular process involved,it is of critical importance that the dual-function catalyst exhibit notonly the capability to initially perform its specified functions, butalso that it has the capability to perform them satisfactorily forprolonged periods of time. The analytical terms used in the art tomeasure how well a particular catalyst performs its intended functionsin a particular hydrocarbon reaction environment are activity,selectivity and stability. And for purposes of discussion here, theseterms are conveniently defined for a given charge stock as follows: (1)activity is a measure of the catalyst's ability to convert hydrocarbonreactants into products at a specified severity level where severitylevel means the specific reaction conditions used--that is, thetemperature, pressure, contact time, and presence of diluents such asH2; (2) selectivity refers to the amount of desired product or productsobtained relative to the amount of reactants charged or converted; (3)stability refers to the rate of change with time of the activity andselectivity parameters--obviously, the smaller rate implying the morestable catalyst. In a reforming process, for example, activity commonlyrefers to the amount of conversion that takes place for a given chargestock at a specified severity level and is typically measured by octanenumber of the C₅ ⁺ product stream, selectivity refers to the amount ofC₅ ⁺ yield that is obtained at a particular activity level; andstability is typically equated to the rate of change with time ofactivity, as measured by octane number of C₅ ⁺ product, and ofselectivity, as measured by C₅ ⁺ yield. Actually, the last statement isnot strictly correct because generally a continuous reforming process isrun to produce a constant octane C₅ ⁺ product with severity level beingcontinuously adjusted to attain this result; and, furthermore, theseverity level is for this process usually varied by adjusting theconversion temperature in the reaction zone so that, in point of fact,the rate of change of activity finds response in the rate of change ofconversion temperature and changes in this last parameter arecustomarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause ofobserved deactivation or instability of a dual-function catalyst when itis used in a hydrocarbon conversion reaction is associated with the factthat coke forms on the surface of the catalyst during the course of thereaction. More specifically in these hydrocarbon conversion processes,the conditions utilized typically result in the formation of heavy, highmolecular weight, black, solid or semi-solid, carbonaceous materialwhich coats the surface of the catalyst and reduces its activity byshielding its active sites from the reactants. In other words, theperformance of this dual-function catalyst is sensitive to the presenceof carbonaceous deposits on the surface of the catalyst. Accordingly,the major problem facing workers in this area of the art is thedevelopment of more active and selective catalytic composites that arenot as sensitive to the presence of these carbonaceous materials and/orhave the capability to suppress the rate of the formation of thesecarbonaceous materials on the catalyst. This sensitivity to formation ofcarbonaceous materials is amplified as practitioners of the art reducepressure and increase the severity of processing units in an attempt toextract the maximum octane-barrels from a given feedstock. Viewed interms of performance parameters, the problem is to develop adual-function catalyst having superior activity, selectivity andstability while operating at pressures less than 125 psig.

OBJECTS AND EMBODIMENTS

Accordingly, it is an object of the present invention to provide animproved catalyst for the reforming of hydrocarbons. A corollaryobjective is to provide a means of preparing the improved catalyst. Itis yet another object to provide an improved catalytic reforming processfor improving the anti-knock properties of a gasoline fraction.

Accordingly, in a broad embodiment the present invention is a catalyticcomposite for the conversion of hydrocarbons comprising a uniformlydispersed platinum component, a uniformly dispersed tin component, asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt, nickel, or iridium, and a halogencomponent on a refractory support having a uniform composition and anominal diameter of at least about 650 microns.

In an alternate embodiment the invention is a method of preparing acatalytic composite comprising compositing a uniformly dispersedplatinum component, a uniformly dispersed tin component, a metalcomponent selected from the group consisting of rhodium, ruthenium,cobalt, nickel or iridium and a halogen component on a refractorysupport having a uniform composition and a nominal diameter of at least650 microns such that said metal component is surface-impregnated ontosaid refractory support.

In yet another embodiment the invention involves a process for thecatalytic reforming of a gasoline fraction naphtha to produce ahigh-octane reformate comprising contacting the gasoline fractionnaphtha and hydrogen at reforming conditions with a catalytic compositecomprising a uniformly dispersed platinum component, a uniformlydispersed tin component, a surface-impregnated metal component selectedfrom the group consisting of rhodium, ruthenium, cobalt, nickel oriridium and a halogen component on a refractory support having uniformcomposition and a nominal diameter of at least about 650 microns.

These as well as other objects and embodiments will become apparent uponreview of the more detailed description of the invention hereinafter setforth.

INFORMATION DISCLOSURE

Several catalytic composites relevant to the composition of the instantinvention are disclosed in the art, however, no reference or combinationof references discloses the unique combination of components of theinstant invention. U.S. Pat. No. 3,651,167 (deRosset) discloses acatalyst composition for the selective hydrogenation of C₄ -acetylenesutilizing a catalyst comprising a Group VIII noble metal, preferablypalladium, deposited on a refractory inorganic oxide carrier materialwherein said Group VIII noble metal is surface-impregnated. Thisreference is totally silent to the advantageous use of asurface-impregnated metal in combination with uniformly dispersedplatinum and tin. Further, it is preferred in this reference that thecatalyst be non-acidic, which is in contradistinction to the instantinvention where it is essential that a halogen component be included inthe catalyst composition. U.S. Pat. No. 3,840,471 (Acres) discloses acatalytic composition containing platinum, rhodium, and a base metalcomposited on an inert material wherein tin may be chosen as one of apossible 25 base metals disclosed. The intended use of this catalyst isfor the oxidation reaction of organic compounds, specifically theoxidation of engine or combustion exhausts. Further, this reference isnot even remotely cognizant of the beneficial effect ofsurface-impregnated rhodium.

Of particular interest is the catalyst disclosed in U.S. Pat. No.3,898,154 (Rausch). This reference discloses a catalytic compositecomprising platinum, rhodium, tin, and a halogen on a porous carriermaterial. The reference, however, teaches that it is an essentialfeature that the rhodium component may be incorporated by any meansknown to result in a uniform dispersion thereof in the carrier material.A similar reference, U.S. Pat. No. 3,909,394 (Rausch), discloses acatalytic composite comprising platinum, ruthenium, and a halogen on aporous support. Additionally, it is disclosed that the catalyst maycomprise a Group IVA metallic component, with a tin component beingspecifically disclosed as one of the possible constituents. Thisreference, however, teaches that it is an essential feature that thecomponents thereof are uniformly distributed throughout the porouscarrier material. In particular, it is taught in the reference that theruthenium component may be incorporated by any means known to result ina uniform dispersion thereof in the carrier material. Accordingly, itcan be seen that the reference contemplates the use of ruthenium,platinum, tin, and halogen with a porous support, however, only with theruthenium uniformly distributed. By way of contrast, it has beendiscovered in the present invention that an improved catalyst isobtained when a metal component selected from the group consisting ofrhodium, ruthenium, cobalt, nickel, or iridium is nonuniformlydispersed, i.e., surface-impregnated. Further, as the surprising andunexpected results of the examples presented hereinafter show, acatalyst with a surface-impregnated metal component demonstratessuperior performance when compared to a prior art catalyst having thesame metal uniformly dispersed.

DETAILED DESCRIPTION OF THE INVENTION

To reiterate briefly, in one embodiment the present invention is acatalytic composite for the conversion of hydrocarbons comprising auniformly dispersed platinum component, a uniformly dispersed tincomponent, a surface-impregnated metal component selected from the groupconsisting of rhodium, ruthenium, cobalt, nickel, or iridium, and ahalogen component on a refractory support having a nominal diameter ofat least about 650 microns.

Accordingly, considering first the refractory support utilized in thepresent invention, it is preferred that the material be a porous,adsorptive, high-surface area support having a surface area of about 25to about 500 m² /g. The porous carrier material should also be uniformin composition and relatively refractory to the conditions utilized inthe hydrocarbon conversion process. By the term "uniform in composition"it is meant that the support be unlayered, has no concentrationgradients of the species inherent to its composition, and is completelyhomogenous in composition. Thus, if the support is a mixture of two ormore refractory materials, the relative amounts of these materials willbe constant and uniform throughout the entire support. It is intended toinclude within the scope of the present invention carrier materialswhich have traditionally been utilized in dual-function hydrocarbonconversion catalysts such as: (1) activated carbon, coke, or charcoal;(2) silica or silica gel, silicon carbide, clays and silicates includingthose synthetically prepared and naturally occurring, which may or maynot be acid treated, for example, attapulgus clay, diatomaceous earth,fuller's earth, kaoline, kieselguhr, etc.; (3) ceramics, porcelain,bauxite; (4) refractory inorganic oxides such as alumina, titaniumdioxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia,thoria, boria, silica-alumina, silica-magnesia, chromia-alumina,alumina-boria, silica-zirconia, etc.; (5) crystalline zeoliticaluminosilicates, such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with multivalent cations; and, (6) combinationsof one or more elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas the gamma-, eta-, and theta-aluminas, with gamma-alumina giving bestresults. In addition, in some embodiments, the alumina carrier materialmay contain minor proportions of other well known refractory inorganicoxides such as silica, zirconia, magnesia, etc.; however, the preferredsupport is substantially pure gamma-alumina. Preferred carrier materialshave an apparent bulk density of about 0.3 to about 0.7 g/cc and surfacearea characteristics such that the average pore diameter is about 20 to300 Angstroms, the pore volume is about 0.1 to about 1 cc/g. In general,excellent results are typically obtained with a gamma-alumina carriermaterial which is used in the form of spherical particles having arelatively small diameter (i.e., typically about 1/16 inch), an apparentbulk density of about 0.5 g/cc, a pore volume of about 0.4 cc/g, and asurface area of about 175 m² /g.

The preferred alumina carrier material is uniform in composition and maybe prepared in any suitable manner and may be synthetically prepared ornatural occurring. Whatever type of alumina is employed it may beactivated prior to use by one or more treatments including drying,calcination, steaming, etc., and it may be in a form known as activatedalumina, activated alumina of commerce, porous alumina, alumina gel,etc. For example, the alumina carrier may be prepared by adding asuitable alkaline reagent, such as ammonium hydroxide to a salt ofaluminum such as aluminum chloride, aluminum nitrate, etc., in an amountto form an aluminum hydroxide gel which, upon drying and calcining, isconverted to alumina.

The refractory support may be formed in any desired shape such asspheres, pills, cakes, extrudates, powders, granules, etc. However, itis a feature of the invention that the support be of sufficient sizesuch that it has a nominal diameter of at least about 650 microns. By"nominal diameter" it is meant the narrowest characteristic dimension.Thus, if the shape of the support is a sphere, the diameter thereof mustbe at least about 650 microns. Alternatively, if the shape is anextruded cylinder, the diameter of the circular face must be at least650 microns and the length of the cylinder must be at least 650 microns.Likewise, if the shape of the catalyst is a cube the length of each sidemust be at least 650 microns. Typically, the preferred nominal diameteris within the range of from about 400 to about 3200 microns. Bestresults are obtained when the support has a diameter of about 1500microns.

For purposes of the present invention a particularly preferred form ofalumina is the sphere; and alumina spheres may be continuouslymanufactured by the well known oil-drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid; combiningthe resulting hydrosol with a suitable gelling agent; and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging and dryingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° toabout 400° F. and subjected to a calcination procedure at a temperatureof about 850° to about 1300° F. for a period of about 1 to about 20hours. This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

One essential ingredient of the subject catalyst is the uniformlydispersed platinum component. This platinum component may exist withinthe final catalytic composite as a compound such as an oxide, sulfide,halide, oxyhalide, etc., in chemical combination with one or more of theother ingredients of the composite or as an elemental metal. Bestresults are obtained when substantially all of this component is presentin the elemental state. Generally this component may be present in thefinal catalyst composite in any amount which is catalytically effectivebut relatively small amounts are preferred. In fact the platinumcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum.

This platinum component may be incorporated in the catalytic compositein any suitable manner, such as coprecipitation or cogelation,ion-exchange, or impregnation, provided that a uniform dispersion of theplatinum component within the carrier material results. The preferredmethod of preparing the catalyst involves the utilization of a soluble,decomposable compound of platinum to impregnate the carrier material.For example, this component may be added to the support by comminglingthe latter with an aqueous solution of chloroplatinic acid. Otherwater-soluble compounds of platinum may be employed in impregnationsolutions and include ammonium chloroplatinate, bromoplatinic acid,platinum dichloride, platinum tetrachloride hydrate, platinumdichlorocarbonyl dichloride, dinitrodiaminoplatinum, etc. Theutilization of a platinum chloride compound, such as chloroplatinicacid, is preferred since it facilitates the incorporation of both theplatinum component and at least a minor quantity of the halogencomponent in a single step. Best results are obtained in the preferredimpregnation step if the platinum compound yields complex anionscontaining platinum in acidic aqueous solutions. Hydrogen chloride orthe like acid is also generally added to the impregnation solution inorder to further facilitate the incorporation of the halogen componentand the distribution of the metallic component. In addition, it isgenerally preferred to impregnate the carrier material after it has beencalcined in order to minimize the risk of washing away the valuableplatinum compounds; however, in some cases it may be advantageous toimpregnate the carrier material when it is in a gelled state.

Yet another essential ingredient of the catalyst of the presentinvention is the uniformly dispersed tin component. This component maybe present as an elemental metal, as a chemical compound such as theoxide, sulfide, halide, oxychloride, etc., or as a physical or chemicalcombination with the porous carrier material and/or other components ofthe catalytic composite. The tin component is preferably utilized in anamount sufficient to result in a final catalytic composite containingabout 0.01 to about 5 wt. percent tin, calculated on an elemental basis,with best results obtained at a level of about 0.1 to about 2 wt.percent. The tin component may be incorporated in the catalyticcomposite in any suitable manner to achieve a uniform dispersion such asby coprecipitation or cogelation with the porous carrier material,ion-exchange with the carrier material or impregnation of the carriermaterial at any stage in the preparation. It is to be noted that it isintended to include within the scope of the present invention allconventional methods for incorporating a metallic component in acatalytic composite. One preferred method of incorporating the tincomponent into the catalytic composite involves coprecipitating the tincomponent during the preparation of the preferred refractory oxidecarrier material. In the preferred case, this involves the addition ofsuitable soluble tin compounds such as stannous or stannic halide to thealumina hydrosol, and then combining the hydrosol with a suitablegelling agent and dropping the resulting mixture into an oil bath, etc.,as explained in detail hereinbefore. Following the calcination step,there is obtained a carrier material having a uniform dispersion ofstannic oxide in an intimate combination with alumina. Another preferredmethod of incorporating the tin component into the catalyst compositeinvolves the utilization of a soluble, decomposable compound of tin toimpregnate and uniformly disperse the tin throughout the porous carriermaterial.

Thus, the tin component may be added to the carrier material bycommingling the latter with an aqueous solution of a suitable tin saltor water-soluble compound of tin such as stannous bromide, stannouschloride, stannic chloride, stannic chloride pentahydrate, stannicchloride tetrahydrate, stannic chloride trihydrate, stannic chloridediamine, stannic trichloride bromide, stannic chromate, stannousfluoride, stannic fluoride, stannic iodide, stannic sulfate, stannictartrate, and the like compounds. The utilization of a tin chloridecompound, such as stannous or stannic chloride is particularly preferredsince it facilitates the incorporation of both the tin component and atleast a minor amount of the preferred halogen component in a singlestep. In general, the tin component can be impregnated either prior to,simultaneously with, or after the other components are added to thecarrier material.

Yet another essential feature of the present invention is asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt and nickel, or iridium. As heretoforenoted, while the prior art has recognized that a platinum-tin reformingcatalyst may advantageously contain a third metal component, it wasbelieved essential that this metal component be uniformly distributedthroughout the catalyst to achieve beneficial results. By way ofcontrast it has now been determined that improved performance may beachieved by incorporating a surface-impregnated metal component into areforming catalyst composite containing uniformly dispersed platinum andtin as opposed to the uniformly distributed metal component of the art.It is to be understood that as utilized herein, the term"surface-impregnated" means that at least 80% of the surface-impregnatedcomponent is located within the exterior surface of the catalystparticle. The term "exterior surface" is defined as the outermost layerof the catalyst, preferably that which comprises the exterior 50% of thecatalyst volume. Expressed in an alternative way, the term "exteriorsurface" is defined as the exterior 0.2 r layer when the catalyst isspherical in shape and 0.3 r when the catalyst is cylindrical in shapeand the length to diameter ratio of the cylinder is greater than orequal to 2:1. In both of these formulae "r" is defined as the nominalradius of the support. However, when the shape of the catalyst is suchthat the determination of the radius is ambiguous, (e.g., a cloverleafshape) then the "exterior surface" is defined as the outermost layer ofthe catalyst comprising the exterior 50% of the catalyst volume. By"layer" it is meant a stratum of substantially uniform thickness.

A metal component is considered surface-impregnated when the averageconcentration of said metal component within the exterior surface of thecatalyst is at least 4 times the average concentration of the same metalcomponent in the remaining interior portion of the catalyst.Alternatively, a metal component is said to be surface-impregnated whenthe average atomic ratio of the metal component to the uniformlydispersed platinum component is at least 4 times greater in magnitudewithin the exterior surface of the catalyst than it is within theremaining interior portion.

As previously stated, the surface-impregnated metal is selected from thegroup consisting of rhodium, ruthenium, cobalt, nickel or iridium. Thesurface-impregnated metal component may be present in the composite asan elemental metal or in chemical combination with one or more of theother ingredients of the composite, or as a chemical compound of themetal such as the oxide, oxyhalide, sulfide, halide, and the like. Themetal component may be utilized in the composite in any amount which iscatalytically effective, with the preferred amount being about 0.01 toabout 2 wt. % thereof, calculated on an elemental metal basis.Typically, best results are obtained with about 0.05 to about 1 wt. % ofsurface-impregnated metal. Additionally, it is within the scope of thepresent invention that beneficial results may be obtained by having morethan one of the above-named metals surface-impregnated on the catalyst.

The surface-impregnated component may be incorporated into the catalyticcomposite in any suitable manner which results in the metal componentbeing concentrated in the exterior surface of the catalyst support inthe preferred manner. In addition, it may be added at any stage of thepreparation of the composite--either during preparation of the carriermaterial or thereafter--and the precise method of incorporation used isnot deemed to be critical so long as the resulting metal component issurface-impregnated as the term is used herein. A preferred way ofincorporating this component is an impregnation step wherein the porouscarrier material containing uniformly dispersed tin and platinum isimpregnated with a suitable metal-containing aqueous solution. It isalso preferred that no "additional" acid compounds are to be added tothe impregnation solution. In a particularly preferred method ofpreparation the carrier material, containing tin and platinum, issubjected to oxidation and halogen stripping procedures, as is explainedhereinafter, prior to the impregnation of the surface-impregnated metalcomponents. Aqueous solutions of water soluble, decomposablesurface-impregnated metal compounds are preferred, includinghexaminerhodium chloride, rhodium carbonylchloride, rhodium trichloridehydrate, ammonium pentachloroaquoruthenate, ruthenium trichloride,nickel chloride, nickel nitrate, cobaltous chloride, cobaltous nitrate,iridium trichloride, iridium tetrachloride and the like compounds.

The catalyst composite of the instant invention is considered by thoseskilled in the art to be an acidic catalyst. Accordingly, it isessential that the catalyst contain a halogen component which imparts tothe composite the necessary acidic function. As hereinabove mentioned,it is preferred that the carrier material containing platinum and tin besubjected to oxidation and halogen stripping procedures prior toaddition of the surface-impregnated metal component. The presence ofexcessive amounts of halogen or halide, for example, chloride, on thecarrier prior to the addition of the surface-impregnated metal, willprevent attainment of the novel surface deposited feature of the instantinvention. The oxidation can be carried out at temperatures from about93° C. (200° F.) to about 593° C. (1100° F.) in an air atmosphere for aperiod of about 0.5 to about 10 hours in order to convert the metalliccomponents substantially to the oxide form. The stripping procedure isconducted at a temperature of from about 371° C. (700° F.) to about 593°C. (1100° F.) in a flowing air/steam atmosphere for a period of fromabout 1 to 10 hours. Following addition of the surface-impregnated metalcomponent, the halogen is then added under oxidative conditions to thecarrier material. Although the precise form of the chemistry of theassociation of the halogen component with the carrier material is notentirely known, it is customary in the art to refer to the halogencomponent as being combined with the carrier material, or with the otheringredients of the catalyst in the form of the halide (e.g., as thechloride). This combined halogen may be fluoride, chloride, iodide,bromide, or mixtures thereof. Of these, fluoride and, particularly,chloride are preferred for the purposes of the present invention. Thehalogen may be added to the carrier material in any suitable mannerafter the addition of the surface-impregnated metal component. Forexample, the halogen may be added as an aqueous solution of a suitabledecomposable halogen-containing compound such as hydrogen fluoride,hydrogen chloride, hydrogen bromide, ammonium chloride, etc. Forreforming, the halogen will be typically combined with the carriermaterial in an amount sufficient to result in a final composite thatcontains about 0.1 to about 3.5 wt. % and preferably about 0.5 to about1.5 wt. % of halogen calculated on an elemental basis.

Another significant parameter for the present catalyst is the 'totalmetals content" which is defined to be the sum of the platinumcomponent, tin component and the surface-impregnated metal component,calculated on an elemental basis. Good results are ordinarily obtainedwith the subject catalyst when this parameter is fixed at a value ofabout 0.2 to about 6 wt. %, with best results ordinarily achieved at ametals loading of about 0.3 to about 2 wt. %.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 93° C. (200° F.) to about 316°C. (600° F.) for a period of from about 2 to about 24 hours or more, andfinally calcined or oxidized at a temperature of about 371° C. (700° F.)to about 593° C. (1100° F.) in an air atmosphere for a period of about0.5 to about 10 hours in order to convert the metallic componentssubstantially to the oxide form. Best results are generally obtainedwhen the halogen content of the catalyst is adjusted during thecalcination step by including water and a halogen or a decomposablehalogen-containing compound in the air atmosphere utilized. Inparticular, when the halogen component of the catalyst is chlorine, itis preferred to use a mole ratio of H₂ O to HCl of about 5:1 to about100:1 during at least a portion of the calcination step in order toadjust the final chlorine content of the catalyst to a range of about0.5 to about 1.5 wt. %.

It is preferred that the resultant calcined catalytic composite besubjected to a substantially water-free reduction step prior to its usein the conversion of hydrocarbons. This step is designed to ensure auniform and finely divided dispersion of the platinum componentthroughout the carrier material. Preferably, substantially pure and dryhydrogen (i.e., less than 20 vol. ppm H₂ O) is used in the reducingagent in this step. The reducing agent is contacted with the calcinedcatalyst at a temperature of about 427° C. (800° F.) to about 649° C.(1200° F.) and for a period of time of about 0.5 to 10 hours or more,effective to reduce substantially all of the platinum component and thesurface-impregnated metal component to the elemental state. However, inthe case where the surface-impregnated metal component is nickel orcobalt, then the surface-impregnated metal may be primarily in the oxideform after the reduction step. This reduction treatment may be performedin situ as part of a startup sequence if precautions are taken to predrythe plant to a substantially water-free state and if substantiallywater-free hydrogen is used.

The resulting reduced catalytic composite may, in some cases, bebeneficially subjected to a presulfiding operation designed toincorporate in the catalytic composite from about 0.05 to about 0.50 wt.% sulfur calculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitablesulfur-containing compound such as hydrogen sulfide, lower molecularweight mercaptans, organic sulfides, etc. Typically, this procedurecomprises treating the reduced catalyst with a sulfiding gas such as amixture of hydrogen and hydrogen sulfide having about 10 moles ofhydrogen per mole of hydrogen sulfide at conditions sufficient to effectthe desired incorporation of sulfur, generally including a temperatureranging from about 10° C. (50° F.) up to about 593° C. (1100° F.) ormore. It is generally a good practice to perform this presulfiding stepoperation under substantially water-free conditions.

According to the present invention a hydrocarbon charge stock andhydrogen are contacted with the trimetallic catalyst described above ina hydrocarbon conversion zone. This contacting may be accomplished byusing the catalyst in a fixed bed system, a moving bed system, afluidized bed system, or in a batch type operation. In the fixed bedsystem, a hydrogen-rich gas and the charge stock are preheated by anysuitable heating means to the desired reaction temperature and then arepassed into a conversion zone containing a fixed bed of the catalysttype previously characterized. It is, of course, understood that theconversion zone may be one or more separate reactors with suitable meanstherebetween to ensure that the desired conversion temperature ismaintained at the entrance to each reactor. It is also important to notethat the reactants may be contacted with the catalyst bed in eitherupward, downward, or radial flow fashion with the latter beingpreferred. In addition, the reactants may be in the liquid phase, amixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase.

In the case where the catalyst of the present invention is used in areforming operation, the reforming system will comprise a reforming zonecontaining a fixed or moving bed of the catalyst types previouslycharacterized. This reforming zone may be one or more separate reactorswith suitable heating means therebetween to compensate for theendothermic nature of the reactions that take place in each catalystbed. The hydrocarbon feed stream that is charged to this reformingsystem will comprise hydrocarbon fractions containing naphthenes andparaffins that boil within the gasoline range. The preferred chargestocks are naphthas, those consisting essentially of naphthenes andparaffins, although in many cases aromatics will also be present. Thispreferred class includes straight run gasolines, natural gasolines,synthetic gasolines, and the like. On the other hand, it is frequentlyadvantageous to charge thermally or catalytically cracked gasolines orhigher boiling fractions thereof. Mixtures of straight run and crackedgasoline range naphthas can also be used to advantage. The gasolinerange naphtha charge stock may be a full boiling gasoline having aninitial boiling point of from about 10° C. (50° F.) to about 66° C.(150° F.) and an end boiling point within the range of from about 163°C. (325° F.) to about 218° C. (425° F.), or may be a selected fractionthereof which generally will be a higher boiling fraction commonlyreferred to as a heavy naphtha--for example, a naphtha boiling in therange of C₇ to 204° C. (400° F.). In some cases it is also advantageousto charge pure hydrocarbons or mixtures of hydrocarbons that have beenextracted from hydrocarbon distillates--for example, straight-chainparaffins--which are to be converted to aromatics. It is preferred thatthese charge stocks be treated by conventional catalytic pretreatmentmethods such as hydrorefining, hydrotreating, hydrodesulfurization,etc., to remove substantially all sulfurous, nitrogenous andwater-yielding contaminants therefrom, and to saturate any olefins thatmay be contained therein.

In a reforming embodiment, it is generally a preferred practice to usethe present catalytic composite in a substantially water-freeenvironment. Essential to the achievement of this condition in thereforming zone is the control of the amount of water and water-producingcompounds present in the charge stock and the hydrogen stream which arebeing charged to the zone. Best results are ordinarily obtained when thetotal amount of water entering the conversion zone from any source isheld to a level substantially less than 50 ppm, and preferably less than20 ppm, expressed as weight of equivalent water in the charge stock. Ingeneral, this can be accomplished by an appropriate pretreatment of thecharge stock coupled with the careful control of the water present inthe charge stock and in the hydrogen stream; the charge stock can bedried by using any suitable drying means known to the art such as aconventional solid adsorbent having a high selectivity for water, forinstance, sodium or calcium crystalline aluminosilicates, silica, gel,activated alumina, molecular sieves, anhydrous calcium sulfate, highsurface area sodium and the like adsorbents. Similarly, the watercontent of the charge stock may be adjusted by suitable strippingoperations in a fractionation column or like device. And in some cases,a combination of adsorbent drying and distillation drying may be usedadvantageously to effect almost complete removal of water from thecharge stock. Preferably, the charge stock is dried to a levelcorresponding to less than 20 ppm of H₂ O equivalent. In general, it ispreferred to control the water content of the hydrogen stream enteringthe hydrocarbon conversion zone within a level of about 5 to 20 vol. ppmof water or less.

In the reforming embodiment, an effluent stream is withdrawn from thereforming zone and passed through a cooling means to a separation zone,typically maintained at about -4° C. (25° F.) to 66° C. (150° F.),wherein a hydrogen-rich gas is separated from a high octane liquidproduct, commonly called an "unstabilized" reformate. When the watercontent of the hydrogen-rich gas is greater than desired, a portion ofthis hydrogen-rich gas is withdrawn from the separating zone and passedthrough an adsorption zone containing an adsorbent selective for water.The resultant substantially water-free hydrogen stream is then recycledthrough suitable compressing means back to the reforming zone. If thewater content of the hydrogen-rich gas is within the range specified,then a substantial portion of it can be directly recycled to thereforming zone, the liquid phase from the separating zone is typicallywithdrawn and commonly treated in a fractionating system in order toadjust the butane concentration, thereby controlling front-endvolatility of the resulting reformate.

The conditions utilized for the reforming embodiment of the presentinvention include a pressure selected from the range of about 101 kPa (0psig) to about 6995 kPa (1000 psig), with the preferred pressure beingabout 446 kPa (50 psig) to about 2514 kPa (350 psig). Particularly goodresults are obtained at low pressure, namely, a pressure of about 446kPa (50 psig) to 791 kPa (100 psig). In fact, it is a singular advantageof the present invention that it allows stable operation at lowerpressures than have heretofore been successfully utilized in so-called"continuous" reforming systems with a bimetallic catalyst (i.e.,reforming for periods of about 0.5 to about 5 or more barrels of chargeper pound of catalyst without regeneration). In other words, thecatalyst of the present invention allows the operation of a continuousreforming system to be conducted at lower pressure (i.e., about 50 psig)for about the same or better catalyst life before regeneration as hasbeen heretofore realized with conventional bimetallic catalysts athigher pressures (i.e., 125 psig).

Similarly, the temperature required for reforming with the subjectcatalyst is generally lower than that required for a similar reformingoperation using a high quality bimetallic platinum catalyst of the priorart. This significant and desirable feature of the present invention isa consequence of the selectivity of the catalyst of the presentinvention for the octane-upgrading reactions that are preferably inducedin a typical reforming operation. Hence, reforming conditions include atemperature in the range of from about 427° C. (800° F.) to about 593°C. (1100° F.) and preferably about 482° C. (900° F.) to about 566° C.(1050° F.) As is well known to those skilled in the continuous reformingart, the initial selection of the temperature within this broad range ismade primarily as a function of the desired octane of the productreformate considering the characteristics of the charge stock and thecatalyst. Ordinarily, the temperature then is thereafter slowlyincreased during the run to compensate for the inevitable deactivationthat occurs to provide a constant octane product.

It is a feature of the present invention that the rate at which thetemperature is increased in order to maintain a constant octane productis substantially lower for the catalyst of the present invention.Moreover, for the catalyst of the present invention, the C₅ ⁺ yield lossfor a given temperature increase is substantially lower than for a highquality bimetallic reforming catalyst of the prior art. In addition,hydrogen production is substantially higher.

The reforming conditions of the present invention also includesufficient hydrogen to provide an amount of about 1 to about 20 moles ofhydrogen per mole of hydrocarbon entering the reforming zone, withexcellent results being obtained when about 5 to about 10 moles ofhydrogen are used per mole of hydrocarbon. The liquid hourly spacevelocity (LHSV) included in the reforming conditions employed in theinvention is selected from the range of about 0.1 to about 10 hr.⁻¹ witha value in the range of about 1 to about 5 hr.⁻¹ being preferred. Infact, the present invention allows operations to be conducted at ahigher LHSV than normally can be stably achieved in a continuousreforming process with a high quality bimetallic platinum reformingcatalyst of the prior art. This last feature is of immense economicsignificance because it allows a continuous reforming process to operateat the same throughput level with less catalyst inventory than thatheretofore used with conventional reforming catalysts at no sacrifice incatalyst life before regeneration.

The following working examples are given to illustrate further thepreparation of the catalytic composite of the present invention and theuse thereof in the conversion of hydrocarbons. It is understood that theexamples are intended to be illustrative rather than restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical depiction of Catalyst A, made in accordance withthe invention, comparing the distribution profiles of platinum and tinbeing uniformly dispersed to rhodium being nonuniformly dispersedthrough the catalyst particle of the present invention.

FIG. 2 is a graphical depiction of Catalyst B, not of the instantinvention, showing the distribution profiles of platinum, tin andrhodium, all being uniformly dispersed through a catalyst particle ofthe prior art.

FIG. 3 is a graphical depiction of catalyst selectivity as measured bythe C₅ ⁺ reformate volume percent yield as a function of catalyst lifemeasured in barrels of charge stock processed per pound of catalyst.Performance data for both Catalyst A and Catalyst B are shown.

FIG. 4 is a graphical depiction of catalyst activity as measured byaverage reaction zone temperature necessary to provide a reformate of102 research octane number as a function of catalyst life measured inbarrels of charge stock processed per pound of catalyst. Again,performance data for both Catalyst A and Catalyst B are shown.

EXAMPLE I

This example sets forth a preferred method of preparing the catalyticcomposite of the present invention. A tin-containing alumina sphere wasprepared by cogelling an alumina hydrosol containing a soluble compoundof tin by the oil-drop method. After oil-dropping and aging the cogelledspheres were dried and calcined. The resulting particles compriseduniformly distributed tin oxide and alumina in the shape of sphereshaving an approximate diameter of 1500 microns.

An aqueous impregnation solution containing chloroplatinic acid andhydrogen chloride was then prepared. This solution contained hydrogenchloride in an amount corresponding to about 2 wt. % of the carriermaterial to be impregnated. The amount of hydrogen chloride utilized inthe impregnation solution was selected to assure good dispersion ofplatinum throughout the catalyst particle.

The amount of platinum component in the impregnation solution utilizedto make the catalyst of the present invention was sufficient to resultin a finished catalyst composite containing 0.375 wt. % platinum. Afterimpregnation the catalyst was dried and calcined. After calcination thecatalyst was subjected to a chloride stripping procedure to remove anyexcess chloride ions that would have a deleterious effect on thesubsequent rhodium impregnation. As heretofore mentioned, the presenceof excess chloride ions would cause the rhodium to be uniformlydistributed throughout the carrier material and not remain in theexternal 300 micron layer as is essential in the instant invention. Thestripping procedure was conducted at a temperature of about 980° F.(527° C.) by passing a flowing air/steam mixture across the catalystcomposite for approximately 2 hours.

The resulting composite was next contacted with a rhodium-containingaqueous solution prepared by adding rhodium trichloride hydrate to waterin an amount sufficient to result in a composite containing 0.05 wt. %rhodium.

After the rhodium impregnation the catalyst was again dried andcalcined. After calcination the catalyst was subjected to a chlorinationstep to add the halogen component. After chlorination the catalyst wasreduced in a dry hydrogen stream for about 1 hour.

The resulting catalyst particles were analyzed and found to contain, onan elemental basis, about 0.375 wt. % platinum, about 0.05 wt. %rhodium, about 0.3 wt. % tin and about 1.05 wt. % chlorine. Thiscatalyst was designated Catalyst "A". In order to determine whether therhodium component was surface-impregnated Catalyst A was subjected to anelectron microprobe distribution analysis. The results of this analysisare set forth in FIG. 1. As can be noted, FIG. 1 is a normalized ratioof rhodium to aluminum as a function of the distance from the sphereedge in microns. The graph indicates that there is no rhodium beyond adepth of about 150 microns from the sphere edge. Accordingly, it can beseen that Catalyst A comprises a surface-impregnated rhodium component.

EXAMPLE II

In this example a catalyst was made in a fashion such that the rhodiumcomponent was uniformly dispersed throughout the catalyst particle. Theresulting catalyst represents the catalyst compositions of the priorart. The important differences between the procedures used to make theprior art catalyst and Catalyst A are that the prior art procedureutilizes a co-impregnation of platinum and rhodium and does not employ achloride stripping procedure. Accordingly, the catalyst of this examplewas prepared by starting with the same tin-containing alumina as inCatalyst A. A sulfur-free aqueous solution containing chloroplatinicacid, rhodium trichloride hydrate, and hydrogen chloride was thenprepared. Similarly, this solution contained hydrogen chloride in anamount corresponding to about 2 wt. % of the carrier material to beimpregnated. The amount of metallic components in the impregnationsolution utilized to make the catalyst was sufficient to result in afinal composite containing 0.375 wt. % platinum and 0.05 wt. % rhodium.After impregnation, the catalyst was dried and calcined in the samemanner as Catalyst A. After calcination, the catalyst was similarlysubjected to a chlorination step to add the halogen component. Afterchlorination, the catalyst was reduced in a dry hydrogen stream forabout 1 hour. The final catalyst composite comprised, on an elementalbasis, about 0.375 wt. % platinum, about 0.05 wt. % rhodium, about 0.3wt. % tin, and about 1.05 wt. % chlorine. This catalyst was designatedCatalyst "B".

In order to determine the rhodium distribution in Catalyst B, Catalyst Bwas subjected to an electron microprobe distribution analysis. Theresults of this analysis are set forth in FIG. 2. FIG. 2 is a graph ofthe ratio of the counts of rhodium at a given distance from the sphereedge divided by the counts of aluminum detected by the microprobe scan.The data in FIG. 2 clearly reveals that substantial amounts of rhodiumare dispersed in the catalyst at a depth greater than 150 microns, and,in fact, rhodium is uniformly dispersed throughout the catalyst.Accordingly, the rhodium component of Catalyst B is notsurface-impregnated.

EXAMPLE III

In order to compare Catalyst A, a composite made in accordance with theinvention, with Catalyst B, a catalyst not having a surface-impregnatedrhodium component, both catalysts were separately subjected to a highstress evaluation test designed to determine the relative activity andselectivity for the reforming of a gasoline charge stock. In all teststhe same charge stock was utilized, its characteristics are given in thetable below.

                  TABLE I    ______________________________________    PROPERTIES OF PLATEAU UINTA    BASIN NAPHTHA    ______________________________________    IBP, °C. (°F.)                     80 (176)    50%             121 (250)    EP              199 (390)    Paraffins, Vol %                    66    Naphthenes, Vol %                    24    Olefins, Vol %  --    Aromatics, Vol %                    10    API               58.7    Sulfur          <0.5 wt. ppm    H.sub.2 O       10 wt. ppm    Cl               1 wt. ppm    Nitrogen        <13 wt. ppm    ______________________________________

The tests were performed in a laboratory scale reforming plantcomprising a reactor containing a catalyst undergoing evaluation, ahydrogen separating zone, a debutanizer column, suitable heating,pumping, and condensing means, etc.

In this plant, a hydrogen recycle stream and a charge stock arecommingled and heated to the desired conversion temperature. Theresulting mixture is then passed downflow into a reactor containing thecatalyst being tested as a fixed bed. An effluent stream is thenwithdrawn from the bottom of the reactor, cooled to about 0° C. (32° F.)and passed to the separating zone wherein a hydrogen-rich gaseous phaseseparates from a liquid phase. The hydrogen-rich gaseous phase is thenwithdrawn from the separating zone and a portion of it is continuallypassed through a high surface area sodium scrubber. The resultingsubstantially water-free hydrogen stream is then recycled to the reactorin order to supply hydrogen for the reaction. The excess hydrogen overthat needed for recycle is recovered as excess separator gas. Moreover,the liquid phase from the separating zone is withdrawn therefrom andpassed to the debutanizer column wherein light ends are taken overheadas debutanizer gas and a C₅ ⁺ reformate stream recovered as bottoms.

The conditions utilized in both tests were a reaction zone outletpressure of about 50 psig, a 5.0 molar ratio of hydrogen-rich vapor tohydrocarbon charge stock, and a 2.0 liquid hourly space velocity.Reaction zone temperatures were selected to achieve a hydrocarbonproduct reformate of 102 research octane number. The results of testingof Catalysts A and B are set forth in FIGS. 3 and 4.

FIG. 3 is a graphical depiction of the C₅ ⁺ liquid volume percent yield,based on the volume of hydrocarbon charge stock, as a function ofcatalyst life as measured by the barrels of charge stock processed perpound of catalyst. Surprisingly and unexpectedly Catalyst A, containinga surface-impregnated rhodium component consistently exhibits a higherC₅ ⁺ liquid volume percent yield of 102 research octane numberreformate. Accordingly, Catalyst A exhibits improved selectivity for theproduction of 102 research octane number reformate relative to CatalystB. FIG. 4 is a graphical depiction of the average reactor inlettemperature necessary to achieve a reformate of 102 research octanenumber as a function of catalyst life defined as barrels of charge stockprocessed per pound of catalyst. Using the average inlet temperature asa measure of catalyst activity, it can be seen that surprisingly andunexpectedly Catalyst A, having a surface-impregnated rhodium component,exhibits a higher activity (lower average reactor inlet temperature)than is exhibited by Catalyst B. More importantly, Catalyst A exhibitsgreater activity stability as measured by the slope of the averagereactor inlet temperature line. Thus, comparing the performance of thetwo catalysts at a given end-of-run temperature, for example, 990° F.(532° C.), shows that Catalyst A processed 124% more charge stock thandid Catalyst B. In other words, Catalyst A had more than twice thestability as that of Catalyst B. Accordingly, Catalyst B showed muchgreater loss of activity as measured by the respective slopes of theinlet temperature lifelines.

EXAMPLE IV

The catalyst described in this example represents another catalystcomposite of the present invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared by following the procedureoutlined in Example I. An impregnation solution containing ammoniumpentachloroaquoruthenate and water was contacted with the platinum andtin containing spherical particles in a manner to result in a compositecontaining 0.5 wt. % surface-impregnated ruthenium. After the rutheniumimpregnation, the catalyst was dried and calcined. After calcination,the composite was subjected to a chlorination step to add the halogencomponent. After chlorination, the catalyst was reduced in a dryhydrogen stream for about 1 hour.

The resulting catalyst particles were found to contain, on an elementalbasis, about 0.375 wt. % uniformly dispersed platinum, about 0.5 wt. %surface-impregnated ruthenium, about 0.3 wt. % uniformly dispersed tinand about 1.05 wt. % chlorine. This catalyst was designated as Catalyst"C".

EXAMPLE V

To illustrate clearly the benefits of surface-impregnated ruthenium, acatalyst composite with uniformly dispersed ruthenium was prepared forcomparison. In making this uniformly dispersed ruthenium-containingcatalyst, a uniformly dispersed tin containing alumina support,identical to that used for preparing Catalyst "C" was contacted with animpregnation solution containing chloroplatinic acid, rutheniumtrichloride, and 12 wt. % hydrogen chloride based on the weight of thecarrier material. This high acid solution was selected to assure auniform dispersion of both the platinum and ruthenium. The drying,calcining, and halogen addition steps were identical to that used forCatalyst "C". Accordingly, this catalyst was made in accordance with theteachings of U.S. Pat. No. 3,909,394. The final catalyst compositecomprised, on an elemental basis, about 0.375 wt. % uniformly dispersedplatinum, about 0.5 wt. % uniformly dispersed ruthenium, about 0.3 wt. %uniformly dispersed tin, and about 1.05 wt. % chlorine. This catalystwas designated Catalyst "D".

EXAMPLE VI

In order to compare Catalyst "C", a composite made in accordance withthe invention with Catalyst "D", a catalyst not having asurface-impregnated metal component, both catalysts were testedfollowing the procedure outlined in Example III.

The performance results are presented in Table II. It is observed that,at the completion of a 45° F. (7° C.) temperature cycle, Catalyst "C"produces slightly higher C₅ ⁺ liquid volume percent yield of 102research octane number reformate than does the uniformly dispersedruthenium catalyst. More importantly, Catalyst "C", havingsurface-impregnated ruthenium, is much more activity stable as evidencedby the lower ratio of temperature to barrels of feed processed per poundof catalyst loaded and is capable of processing about 30% more feed thanCatalyst B for the same temperature cycle. In other words, the uniformlydispersed ruthenium catalyst, Catalyst "D", deactivated about 35% fasterthan the catalyst composite of the instant invention.

                  TABLE II    ______________________________________    Catalyst          C        D    ______________________________________    Ru Impregnation   Surface  Uniform    Start of Run Temp.                      960      964    @ 0.3 BPP, °F.    Avg. C.sub.5.sup.+ Liq. Yield,                      79.3     79.1    wt. %    Deactivation Rate,                      35.7     48.4    °F./BPP    ______________________________________

EXAMPLE VII

The catalyst described in this example represents another catalystcomposite of the instant invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared following the procedureoutlined in Example I. An impregnation solution containing nickelnitrate and isopropanol was contacted with the platinum and tincontaining spherical particles in a manner to result in a compositecontaining 0.36 wt. % surface-impregnated nickel. After the nickelimpregnation, the catalyst was dried and calcined. After calcination,the catalyst was subjected to a chlorination step to add the halogencomponent. After chlorination, the catalyst was reduced in a dryhydrogen stream for about 1 hour.

The resulting catalyst particles were found to contain 0.387 wt. %uniformly dispersed platinum, 0.36 wt. % surface-impregnated nickel, 0.3wt. % uniformly dispersed tin and 1.05 wt. % chlorine. This catalyst wasdesignated as Catalyst "E".

EXAMPLE VIII

To illustrate the advantages of having surface-impregnated nickel, acatalyst composite was prepared for comparison wherein the nickel wasuniformly dispersed throughout the catalyst composite. In preparation ofthe uniformly dispersed nickel containing catalyst, a uniformlydispersed tin containing alumina support, identical to that used forpreparing Catalyst "E", was contacted with an impregnation solutioncontaining chloroplatinic acid, nickel nitrate, and 2 wt. % hydrogenchloride based on the weight of the alumina carrier material. Thishydrogen chloride level was selected to allow for uniform dispersion ofboth the platinum and nickel metals. The drying, calcining, and halogenaddition steps were identical to that used for Catalyst "E". The finalcatalyst composite comprised, on an elemental basis, 0.39 wt. %uniformly dispersed platinum, 0.36 wt. % uniformly dispersed nickel, 0.3wt. % uniformly dispersed tin, and 1.14 wt. % chlorine. This catalystwas designated Catalyst "F".

EXAMPLE IX

The catalyst described in this example represents another catalystcomposite of the instant invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared following the procedureoutlined in Example I. An impregnation solution containing cobaltouschloride and isopropanol was contacted with the platinum and tincontaining spherical particles in a manner to result in a compositecontaining 0.42 wt. % surface-impregnated cobalt. After the cobaltimpregnation, the catalyst was subjected to the identical finishingconditions as those used in Example VII.

The resulting catalyst particles were found to contain 0.384 wt. %uniformly dispersed platinum, 0.42 wt. % surface-impregnated cobalt, 0.3wt. % uniformly dispersed tin and 1.03 wt. % chlorine. This catalyst wasdesignated Catalyst "G".

EXAMPLE X

Catalysts "E", "F" and "G" were performance tested in the identicalmanner as set forth in Example III. Tables III and IV present theresults. Comparing Catalyst "E" to Catalyst "F", as listed in Table III,shows that the surface-impregnated nickel catalyst surprisingly andunexpectedly exhibited an average 4.1 greater C₅ ⁺ liquid volume percentyield of 102 research octane number reformate compared to Catalyst "F"having uniformly dispersed nickel. More importantly, thesurface-impregnated catalyst deactivates at a much lower rate than theuniformly dispersed nickel catalyst, resulting in an activity stabilityimprovement of 48%. This stability improvement allows for 56% morefeedstock to be processed in a given 30° F. temperature cycle by thecatalyst of the instant invention compared to the uniformly dispersednickel containing catalyst.

Test results for Catalyst "G", shown in Table IV, similarly illustrateexceptional performance, thus demonstrating the surprising benefitrealized when surface-impregnated cobalt is employed with uniformlydispersed platinum and tin.

                  TABLE III    ______________________________________    Catalyst          E        F    ______________________________________    Ni Impregnation   Surface  Uniform    Start of Run Temp.                      955      958    @ 0.3 BPP, °F.    Avg. C.sub.5.sup.+ Liq. Yield,                      83.4     79.3    wt. %    Deactivation Rate,                      28.6     42.9    °F./BPP    ______________________________________

                  TABLE IV    ______________________________________    Catalyst          G    ______________________________________    Co Impregnation   Surface    Start of Run Temp.                      948    @ 0.3 BPP, °F.    Avg. C.sub.5.sup.+ Liq. Yield,                      80.6    wt. %    Deactivation Rate,                      17.6    °F./BPP    ______________________________________

In summary, it can be seen from the above performance test results thatby incorporating a surface-impregnated metal component in accordancewith the invention, a superior and improved reforming catalyst isthereby achieved.

What is claimed is:
 1. A catalytic composite for the conversion ofhydrocarbons comprising a uniformly dispersed platinum component, auniformly dispersed tin component, a surface-impregnated metal componentselected from the group consisting of rhodium, ruthenium, cobalt,nickel, or iridium and mixtures thereof and a halogen component on arefractory support having a uniform composition and a nominal diameterof at least 650 microns.
 2. The catalytic composite of claim 1 furthercharacterized in that the refractory support comprises alumina.
 3. Thecatalytic composite of claim 1 further characterized in that the halogencomponent comprises a chlorine component.
 4. The catalytic composite ofclaim 1 further characterized in that it comprises, on an elementalbasis, from about 0.05 to about 1 wt. % platinum, from about 0.05 toabout 1 wt. % surface-impregnated metal, from about 0.1 to about 2 wt. %tin, and from about 0.5 to about 1.5 wt. % chlorine on a support havinga nominal diameter ranging from about 400 to about 3200 microns.
 5. Thecatalytic composite of claim 1 further characterized in that at least80% of the surface-impregnated metal component is deposited within theexterior 50% by volume of said refractory support.
 6. A method ofpreparing a catalytic composite comprising compositing a uniformlydispersed platinum component, a uniformly dispersed tin component, ametal component selected from the group consisting of rhodium,ruthenium, cobalt, nickel, iridium and mixtures thereof and a halogencomponent on a refractory support having a uniform composition and anominal diameter of at least 650 microns such that said metal componentis surface-impregnated onto said refractory support.
 7. The method ofclaim 6 further characterized in that the surface-impregnated componentis added to the catalyst after the addition of the platinum componentbut prior to the addition of the halogen component.
 8. The method ofclaim 6 further characterized in that the refractory support comprisesalumina formed by gelation.
 9. The method of claim 8 furthercharacterized in that the tin component is composited by means of acogelation step during formation of the alumina support.
 10. The methodof claim 6 further characterized in that a halogen stripping procedureis performed prior to the addition of the metal component.